[material_ui] Add splashRadius property to BottomNavigationBar and BottomNavigationBarThemeData

[Mairramer]

as title
Closes flutter/flutter#117957

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[Mairramer]

/gemini review

[gemini-code-assist]

Code Review

This pull request introduces a splashRadius property to BottomNavigationBar and BottomNavigationBarThemeData to allow customization of the ink splash radius for bottom navigation bar items, along with associated tests and changelog updates. The review feedback suggests updating the assertion for splashRadius to use the double literal 0.0 instead of the integer 0 to maintain consistency with other assertions in the constructor.

[gemini-code-assist]

Code Review

This pull request adds a splashRadius property to BottomNavigationBar and BottomNavigationBarThemeData, allowing customization of the ink splash radius for item tap effects. It also adds comprehensive unit tests to verify default values, custom configurations, assertions, and theme overrides. No review comments were provided, so there is no additional feedback.

[QuncCccccc]

BottomNavigationBar is a bit old and should be replaced by NavigationBar in M3. In Material Design 3 and expressive, we don't support splash feature, so I'm closing this PR since this feature doesn't align with the latest design specs.